This invention pertains to apparatus and methods for providing supplemental respirating gas, such as oxygen, to an in vivo respiratory system.
U.S. patent application Ser. No. 210,654, filed Nov. 26, 1980 now U.S. Pat. No. 4,457,303 by Gerald P. Durkan and commonly assigned herewith, is incorporated herein by reference as illustrating a method of supplying respirating gas wherein a pulse of gas is supplied to an in vivo respiratory system substantially at the beginning of inspiration. U.S. patent application Ser. No. 210,654 also discloses a primarily fluidically-operated apparatus comprising a demand gas circuit. The fluidic apparatus comprising the demand gas circuit carries out the method described above and, by virtue of the method, is significantly smaller and more compact than other demand gas-type apparatus which supply respirating gas essentially throughout the duration of inspiration. While this fluidic apparatus has proven extremely effective in such products as home oxygen concentrators and oxygen dillusion or delivery systems, for example, a further reduction in overall apparatus size would further enhance the utility of such products.
Many devices, including those depicted in U.S. patent application Ser. No. 210,654, are adapted to monitor or sense pressure direction in an in vivo respiratory system throughout the respiratory cycle and to selectively supply gas in accordance with the pressure direction in the in vivo respiratory system. In this respect, the in vivo respiratory system creates a negative pressure when an attempt is made to inspire and create positive pressure when an attempt is made to exhale. In certain instances it is advantageous to supply pulses of gas such as these described in the application Ser. No. 210,654 but in such a manner that a pulse is not necessarily supplied for every detection of negative pressure in the in vivo respiratory system. For example, should the in vivo respiratory system attempt to inspire too frequently, an apparatus operating strictly in the manner described in U.S. patent application Ser. No. 210,654 would in some instances cause the in vivo respiratory system to overoxygenate. While breathing rate control circuits and override circuits have been disclosed in the prior art (such as U.S. Pat. Nos. 4,206,754 to Cox and 4,141,754 to Ismach, for example) these circuits are incompatable with the device described in the referenced application.
U.S. patent application Ser. No. 210,654 also illustrates the usage of a "split" or "double hose" cannula which interfaces the in vivo respiratory system through the nares with the sensing and gas supply elements of the apparatus disclosed therein. Although the apparatus performs superbly using the double hose cannula, employment of a single hose cannula rather than a double hose cannula would enable both the sensing of the pressure direction in the in vivo respiratory system and the delivery of respirating gas to the in vivo respiratory system to be accomplished through the same hose. Single hose cannulae, being less expensive to manufacture and more convenient for the physician and user, are generally more prevalent on the market than double hose cannulae. Thus, it would be advantageous to adapt systems such as that disclosed in the referenced application for compatibility with a single hose cannula.
Moreover, it is generally preferable to humidify respirating gas before supplying the gas to an in vivo respiration system. In some circumstances it is desirable to nebulize the respirating gas with medication before supplying the gas to the in vivo respiration system. Although humidifiers and nebulizers have long been used with oxygen supply systems, it is not evident from the prior art how a humidifier or nebulizer can be appropriately utilized with apparatus such as those described in U.S. patent application Ser. No. 210,654, especially if apparatus of that type are used with a single hose cannula as discussed above. A great danger in utilizing humidifiers and/or nebulizers with either single or double hose cannula systems is the transfer of moisture through the hose leading to sensing means used to determine the direction of pressure in the in vivo system. Moisture in the hose leading to the sensing means contaminates the sensor and tends to considerably shorten the life of the sensor.
In some situations it may also be desirable to supply another gas, such as an anesthetic gas, to in vivo respiratory system along with the supply of respirating gas. In such situations, the dosage of second gas must usually be in controlled relation to the amount of respirating gas supplied simultaneously therewith. Moreover, a serious problem results in a demand gas-type device when medicating gas is continually applied regardless of the ability or inability of the in vivo system to demand the respirating gas.
In view of the foregoing, it is an object of the present invention to provide a demand respirating gas supply method and apparatus which prevents overoxygenation by supplying a fixed volume dose of respirating gas per unit time to an in vivo respiratory system.
An advantage of the invention is the provision of a demand respirating gas supply method and apparatus which employs a single hose cannula, thereby allowing pressure sensing and gas supply to be accomplished through the same line.
A further advantage of one embodiment of the invention is the provision of a method and apparatus for supplying spiked shaped pulses of gas at the beginning of an inspiration.
An advantage of another embodiment of the invention is the provision of a method and apparatus for supplying square shaped pulses of gas at the beginning of an inspiration.
Yet another advantage of the invention is the provision of a compact respirating gas supply apparatus.
Still another advantage of the invention is the employment of humidifiers, nebulizers, and the like without deleterious impact upon a sensor used in a respirating supply gas apparatus.